problem 40 // project euler

Champernowne’s constant

An irrational decimal fraction is created by concatenating the positive integers:

It can be seen that the 12^th digit of the fractional part is 1.

If d_n represents the n^th digit of the fractional part, find the value of the following expression.

钱珀瑙恩常数

将所有正整数连接起来构造的一个十进制无理数如下所示：

可以看出小数点后第12位数字是1。

如果d_n表示上述无理数小数点后的第n位数字，求下式的值：